Mind Hacks

Hack #6. Neuropsychology, the 10% Myth, and Why You Use All of Your Brain

Neuropsychology is the study of what different parts of the brain do by studying people who no longer have those parts. As well as being the oldest technique of cognitive neuroscience, it refutes the oft-repeated myth that we only use 10% of our brains.

Of the many unscientific nuggets of wisdom about the brain that many people believe, the most common may be the “fact” that we use only 10% of our brains.

In a recent survey of people in Rio de Janeiro with at least a college education, approximately half stated that the 10% myth was true. ¹ There is no reason to suppose the results of a similar survey conducted anywhere else in the world would be radically different. It’s not surprising that a lot of people believe this myth, given how often it is claimed to be true. Its continued popularity has prompted one author to state that the myth has “a shelf life longer than lacquered Spam”. ²

Where does this rather popular belief come from?

It’s hard to find out how the myth started. Some people say that something like it was said by Einstein, but there isn’t any proof. The idea that we have lots of spare capacity is certainly true and fits with our aspirational culture, as well as with the Freudian notion that the mind is mostly unconscious. Indeed, the myth was being used to peddle self-help literature as early as 1929. ³ The neatness and numerological potency of the 10% figure is a further factor in the endurance of the myth.

—A.B.

Neuropsychology is the study of patients who have suffered brain damage and the psychological consequences of that brain damage. As well as being a vital source of information about which bits of the brain are involved in doing which things, neuropsychology also provides a neat refutation of the 10% myth: if we use only 10% of our brains, which bits would you be happy to lose? From neuropsychology, we know that losing any bit of the brain causes you to stop being able to do something or being able to do it so well. It’s all being used, not just 10% of it.

Admittedly we aren’t clear on exactly what each bit of the brain does, but that doesn’t mean that you can do without 90% of it.

Neuropsychology has other uses aside from disproving unhelpful but popularly held trivia. By looking at which psychological functions remain after the loss of a certain brain region, we can tell what brain regions are and are not necessary for us to do different things. We can also see how functions group and divide by looking at whether they are always lost together or lost only in dissimilar cases of brain damage. Two of the famous early discoveries of neuropsychology are two distinct language processing regions in the brain. Broca’s area (named after the neuropsychologist Paul Broca) is in the frontal lobe and supports understanding and producing structure in language. Those with damage to Broca’s area speak in stilted, single words. Wernicke’s area (on the junction between the temporal and parietal lobes and named after Carl Wernicke) supports producing and understanding the semantics of language. People with brain damage to Wernicke’s area can produce grammatically correct sentences, but often with little or no meaning, an incomprehensible “word salad.”

Another line of evidence against the 10% myth is brain imaging research [Hacks #2 through #4], which has grown exponentially in the last couple of decades. Such techniques allow the increased blood flow to be measured in certain brain regions during the performance of cognitive tasks. While debate continues about the degree to which it is sensible to infer much about functional localization from imaging studies, one thing they make abundantly clear is that there are no areas of the brain that are “black holes”—areas that never “light up” in response to some task or other. Indeed, the neurons that comprise the cortex of the brain are active to some degree all the time, even during sleep.

A third line of argument is that of evolutionary theory. The human brain is a very expensive organ, requiring approximately 20% of blood flow from the heart and a similar amount of available oxygen, despite accounting for only 2% of body weight. The evolutionary argument is straightforward: is it really plausible that such a demanding organ would be so inefficient as to have spare capacity 10 times greater than the areas being usefully employed?

Fourth, developmental studies indicate that neurons that are not employed early in life are likely never to recover and behave normally. For example, if the visual system is not provided with light and stimulation within a fairly narrow developmental window, the neurons atrophy and vision never develops. If the visual system is deprived of a specific kind of stimulation, such as vertical lines, it develops without any sensitivity to that kind of stimulus. Functions in other parts of the brain similarly rely on activation to develop normally. If there really were a large proportion of neurons that were not used but were instead lying in wait, likely they would be useless by puberty.

It can be seen, then, that the 10% myth simply doesn’t stand up to critical thinking. Two factors complicate the picture slightly, however; both have been used to muddy the waters around the claim at some stage.

First, people who suffer hydrocephalus in childhood have been seen to have large “holes” in the middle of their brains and yet function normally (the holes are fluid-filled ventricles that are present in every brain but are greatly enlarged in hydrocephalus). This condition has been the focus of sensationalist television documentaries, the thrust of which is that we can get on perfectly well without much of our brains. Such claims are willfully misleading—what such examples actually show is the remarkable capacity of the brain to assign functioning to alternative areas if there are problems with the “standard” areas during a specific time-point in development. Such “neuronal plasticity,” as it is known, is not seen following brain damage acquired in adulthood. As discussed earlier, development of the brain depends on activity—this same fact explains why hydrocephalitic brains can function normally and makes having an unused 90% extremely unlikely.

Second, there is actually a very disingenuous sense in which we do “use” only 10% of our brains. The glial cells of the brain outnumber the neurons by a factor of roughly 10 to 1. Glial cells play a supporting role to the neurons, which are the cells that carry the electrochemical signals of the brain. It is possible, therefore, to note that only approximately 10% of the cells of the cortex are directly involved in cognition.

This isn’t what proponents of the 10% theory are referring to, however. Instead, the myth is almost always a claim about mind, not brain. The claim is analogous to arguing that we operate at only 10% of our potential (although “potential” is so immeasurable a thing, it is misleading from the start to throw precise percentages around).

Uri Geller makes explicit the “untapped potential” interpretation in the introduction to Uri Geller’s Mind-Power Book:

Our minds are capable of remarkable, incredible feats, yet we don’t use them to their full capacity. In fact, most of us only use about 10 per cent of our brains, if that. The other 90 per cent is full of untapped potential and undiscovered abilities, which means our minds are only operating in a very limited way instead of at full stretch.

The confusion between brain and mind blurs the issue, while lending the claim an air of scientific credibility because it talks about the physical brain rather than the unknowable mind.

But it’s just not true that 90% of the brain’s capacity is just sitting there unused. It is true that our brains adjust their function according to experience [[Hack #12]]—good news for the patients studied by neuropsychology. Many of them recover some of the ability they have lost. It is also true that the brain can survive a surprisingly large amount of damage and still sort of work (compare pouring two pints of beer down your throat and two pints of beer into your computer’s hard disk drive for an illustration of the brain’s superior resistance to insults). But neither of these facts mean that you have exactly 90% of untapped potential—you need all your brain’s plasticity and resistance to insult to keep learning and functioning across your life span.

In summary, the 10% myth isn’t true, but it does offer an intuitively seductive promise of the possibility of self-improvement. It has been around for at least 80 years, and despite having no basis in current scientific knowledge and being refuted by at least 150 years of neuropsychology, it is likely to exist for as long as people are keen to aspire to be something more than they are.

End Notes

1. Herculano-Houzel, S. (2002). Do you know your brain? A survey on public neuroscience literacy at the closing of the decade of the brain. The Neuroscientist 8, 98–110.

2. Radford, B. (1999). The ten-percent myth. Skeptical Inquirer. March–April ( http://www.csicop.org/si/9903/ten-percent-myth.html ).

3. You can read all about the 10% myth in Beyerstein, B. L. (1999), Whence cometh the myth that we only use 10% of our brains? In Della Sala (ed.), Mind Myths—Exploring Popular Assumptions About the Mind and Brain. New York: John Wiley and Sons, 4–24, at snopes.com ( http://www.snopes.com/science/stats/10percnt.htm ), and in these two online essays by Eric Chudler, “Do We Use Only 10% of Our Brain?” ( http://faculty.washington.edu/chudler/tenper.html ) and “Myths About the Brain: 10 Percent and Counting” ( http://www.brainconnection.com/topics/?main=fa/brain-myth ).

—Andrew Brown